In many pneumatic and hydraulic applications a constant or predetermined pressure or flow is required. Constant pressure is generally provided by a feedback diaphragm-type pressure regulator or some other device that requires gain and a feedback signal. Constant flow is often achieved by using a choked flow orifice or a supply that has a flow resistance considerably higher than the circuit it operates. In such a manner small changes in the small resistance are even smaller percentage changes of the overall resistance, hence the flow changes are small. This, however, is not sufficient if the supply pressure changes, for in that case the flow is not regulated at all.